How long should piston valves last? We've lubed it a few xs but now that we went to backwash today I was afraid I'd break it by trying to turn it. All we had available was WD-40 which may not have been ideal but we were limited in time so used it. It helped but it was still very hard to turn and lift. Should we get a new piston valve or is there something we can do to increase the life? Thx